208 PROTEIN POISONS 



to make some comparisons here. As has been stated, the 

 strain with which our work was done was highly virulent, 

 killing half-grown guinea-pigs in doses of 0.0000001 c.c. 

 of a twenty-four-hour culture given intraperitoneally. At 

 the same time our old stock culture of the pneumococcus 

 did not kill in doses of less than 1 c.c., and yet the cellular 

 substances of the two, measured by toxicity, were prac- 

 tically the same. This and similar observations with other 

 bacteria lead us to conclude that virulence is measured 

 by rate of multiplication and not by chemical differences 

 in cellular poison content. Moreover, when two animals 

 were killed with the two strains the cells seemed to be as 

 abundant in one as in the other. The more virulent strain 

 multiplies the faster. Virulence may depend upon several 

 factors, but rate of multiplication is certainly one of them, 

 and on a common medium as the animal body this must 

 depend upon the effectiveness of the ferments whose func- 

 tion it is to prepare and utilize the pabulum on which 

 the organism feeds. Our highly virulent strain furnished 

 a cellular substance which killed guinea-pigs in doses of 

 1 to 10,000. Occasionally smaller doses killed. The smallest 

 fatal dose on first injection of which we have a record was 

 1 to 19,000, but the surely fatal minimum was 1 to 10,000, 

 and as we have stated, the less virulent strain of pneumo- 

 coccus furnished cellular substance of the same degree of 

 toxicity. A comparison of the virulent strain of the pneu- 

 mococcus with our strain of colon is also of interest. With 

 our colon bacillus the minimum constantly fatal dose was 

 1 c.c. of a twenty-four-hour bouillon culture. Sometimes 

 a dose of 0.5 c.c. killed, and the smallest fatal dose, as we 

 found it, was 0.25 c.c. This organism yielded a cellular 

 substance, which as a coarsely ground powder always killed 

 1 to 50,000; when finely ground it killed 1 to 75,000, and 

 sometimes as high as 1 to 2,000,000. Our virulent pneumo- 

 coccus killed in 0.0000001 c.c. doses, and yielded a cellular 

 substance which, when ground to the finest possible powder, 

 killed only 1 to 10,000. Surely these are strong arguments 

 for our belief that the pathogenicity of a microorganism is 



